Hydrophilic colloids such as gelatin have many unique and desirable properties that make them especially useful in the preparation of photographic materials. For example, gelatin has high swellability in aqueous media which allows rapid diffusion of compounds in and out of a gelatin-containing photographic layer during film processing. Gelatin is also an excellent dispersing medium for light-sensitive silver halide grains and aqueous gelatin solutions exhibit excellent coating properties and quickly undergo gelation when chilled; all of these properties are critical to the manufacture of photographic films. In addition, crosslinked gelatin layers provide very good physical properties such as resistance to scratch, abrasion, ferrotyping, and blocking.
In recent years, the conditions under which photographic materials are manufactured or utilized have become more demanding. For example, applications for photographic materials have been extended to high humidity and high temperature environments. Under these conditions, conventional photographic materials may not have adequate dimensional stability or resistance to sticking, blocking, and ferrotyping. Recent patents have disclosed photographic systems (for example, Advanced Photographic Systems) where the processed film may be re-introduced into a cassette. This system allows for compact and clean storage of the processed film until such time when it may be removed for additional prints or to interface with display equipment. Storage in the cassette is preferred to facilitate location of the desired exposed frame and to minimize contact with the negative during subsequent usage. U.S. Pat. No. 5,173,739 discloses a cassette to thrust the photographic element from the cassette, eliminating the need to contact the film with mechanical or manual means. Published European Patent Application 0 476 535 A1 describes how the developed film may be stored in such a cassette. The dimensions of such a so-called thrust cassette requires that the processed photographic element is wound tightly and under pressure, causing direct close contact between the front and back sides which may result in ferrotyping, especially at high temperature and high humidity storage conditions. In order to maximize productivity and reduce cost, photographic materials must be manufactured and processed at very high speeds, thus they may be more easily scratched and abraded. These scratches or abrasion marks are visible during printing or projection of the photographic material.
Various methods have been described to improve the physical properties of hydrophilic colloid-containing layers used in imaging. For example, U.S. Pat. No. 3,240,604 describes a gelatin layer containing discrete poly(tetrafluoroethylene) granules present in a concentration range of 0.05 to 10 parts of poly(tetrafluoroethylene) per part gelatin. U.S. Pat. No. 4,266,015 describes a light sensitive material which includes an outermost layer comprising a fluorine-containing homopolymer or copolymer. Due to their very hydrophobic nature, these fluoropolymers are not very compatible with coating solutions containing a hydrophilic colloid such as gelatin. In addition, these polymer particles can fall-off in processing solutions due to their weak interaction with the hydrophilic colloid binder.
The addition of latex polymers prepared from ethylenically unsaturated monomers to hydrophilic colloid-containing layers to achieve improved properties such as, increased dimensional stability, reduced curl, decreased pressure sensitivity, improved dryability, and improved scratch resistance, is described, for example, in Research Disclosure No. 38957, September 1996, page 601. However, when a large amount of the latex is added to the gelatin, the latex may flocculate. In addition, when a large amount of the latex is added to the hydrophilic colloid-containing outermost protective layer, the latex, especially if it is a low Tg latex, may cause sticking and blocking of the photographic material when it is stored at high temperature.
Methods have been described that reportedly improve the compatibility between the latex polymer and the hydrophilic colloid in order to prevent flocculation of the latex and to improve the adhesion between the latex polymer and the hydrophilic colloid. For example, in U.S. Pat. Nos. 4,855,219, 5,066,572, 5,248,558, 5,330,885, and others, gelatin-coated latex polymers and gelatin-grafted latex polymers and their use in photographic elements are described. Typically, these latex polymers are either soft or hard (meth)acrylate copolymer latexes that provide good, but, not outstanding resistance to scratch, abrasion, and ferrotyping. Therefore, there continues to be a need to further improve the physical performance of photographic materials without sacrificing coating solution stability, surface tackiness, etc. It is toward such an objective that the present invention is directed.